2 Answers
2

Since you only had 8G of free extents after you vgextended you only get a lv representing that absolute size of 8G.

You must inform LVM you intend to make an additional space size. From the manpage of lvextend;

-l, --extents [+]LogicalExtentsNumber[%{VG|LV|PVS|FREE|ORIGIN}]
Extend or set the logical volume size in units of logical
extents. With the '+' sign the value is added to the actual
size of the logical volume and without it, the value is taken as
an absolute one.

Agree with your diagnosis. It's difficult to debug exactly; the lvextend command-line given doesn't seem to work on my test box (debian testing). sudo lvextend -l 100%FREE /dev/mapper/vg_brick-lv_TEST seemed to work fine for me. Specifying it in PEs would be a reasonable alternative tho. It's almost as if the command used was more like lvextend -l 100%LV. Though that should have been obvious - it told me New size (1 extents) matches existing size (1 extents) Run lvextend --help' for more information.`.
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sourcejediApr 23 '13 at 16:42

@alexd @sourcejedi I have updated the question with all the lvextend I ran. Indeed the original one did not work. Eventually I ran lvextend -r -l 100%FREE /dev/ubuntudevbox2/root.
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Anthony KongApr 23 '13 at 20:04